Knee flexion and extension gap tensioning and measuring apparatus

ABSTRACT

A knee gap tensioning apparatus includes: a gap tensioner including: a baseplate; a top plate; a linkage interconnecting the baseplate and the top plate and operable to move the gap tensioner between retracted and extended positions; and wherein the top plate is pivotally connected to the linkage so as to be able to freely pivot about a pivot axis.

This invention relates generally to medical devices and instruments, andmore particularly to a method for applying tension along or across ahuman knee joint to take measurements to repair, augment, or replace it.

BACKGROUND

Total knee arthroplasty (“TKA”) is a procedure for treating an injured,diseased, or worn human knee joint. In a TKA, an endoprosthetic joint isimplanted, replacing the bearing surfaces of the joint with artificialmembers. Proper alignment of the joint and substantially equal tensionin the soft tissues surrounding the joint are important factors inproducing a good surgical outcome.

A human knee joint “J” is shown in FIG. 1-4. The joint J is prepared forimplantation by cutting away portions of the femur “F” and the tibia“T”. FIGS. 1 and 2 show the joint in extension, with cutting planes fora tibial cut 1 and a distal femoral cut 2. The tibial cut 1 and thedistal formal cut 2 cooperate to define an extension gap “EG”. FIGS. 3and 4 show the joint J in flexion, with cutting plane 3 for a posteriorcut. The tibial cut 1 and the posterior cut 3 cooperate to define aflexion gap “FG”.

A goal of total knee arthroplasty is to obtain symmetric and balancedflexion and extension gaps FG, EG (in other words, two congruentrectangles). These gaps are generally measured in millimeters ofseparation, are further characterized by a varus or valgus anglemeasured in degrees, and are measured after the tibia cut, distalfemoral cut, and posterior femoral cut have been done (to create flatsurfaces from which to measure). It follows that, to achieve thisbalance, the ligament tension in the lateral and medial ligaments wouldbe substantially equal on each side, and in each position; it alsofollows that the varus/valgus angle in flexion and extension would be0°.

Some surgeons favor the use of a measured resection technique in whichbone landmarks, such as the transepicondylar, the anterior-posterior, orthe posterior condylar axes are used to determine proper femoralcomponent rotation and subsequent gap balance. Others favor a “gapbalancing technique” in which the femoral component is positionedparallel to the resected proximal tibia with each collateral ligamentsubstantially equally tensioned to obtain a rectangular flexion gap.

One problem with prior art balancing techniques is that it is difficultand complex to achieve the proper balance. Current state-of-the-art gapbalancing devices do not enable balancing with the patella in-place andare large, overly-complicated devices that work only with theirrespective knee systems.

BRIEF SUMMARY OF THE INVENTION

This problem is addressed by a gap tensioner operable to apply a load toa gap between the bones of a joint and measure the resulting gapdistance and angle between the bones.

According to one aspect of the invention, a knee gap tensioningapparatus includes: a gap tensioner including: a baseplate; a top plate;a linkage interconnecting the baseplate and the top plate and operableto move the gap tensioner between retracted and extended positions; andwherein the top plate is pivotally connected to the linkage so as to beable to freely pivot about a pivot axis.

According to another aspect of the invention, a knee gap tensioningapparatus includes: a gap tensioner including: a baseplate; a top plate;a linkage interconnecting the baseplate and the top plate and operableto move the gap tensioner between retracted and extended positions; andwherein the top plate is pivotally connected to the linkage so as to beable to freely pivot about a pivot axis; two or more tracking markers,at least one of which is coupled to the gap tensioner; an electronicreceiving device, wherein the receiving device is operable incombination with the tracking markers to determine a position andorientation of each of the tracking markers relative to the electronicreceiving device.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be best understood by reference to the followingdescription taken in conjunction with the accompanying drawing figuresin which:

FIG. 1 is a view of the anterior aspect of the human knee joint inextension showing cutting planes for a total knee arthroscopy;

FIG. 2 is a view of the lateral aspect of the human knee joint of FIG.1;

FIG. 3 is a view of the anterior aspect of the human knee joint inflexion showing cutting planes for a total knee arthroscopy;

FIG. 4 is a view of the lateral aspect of the human knee joint of FIG.3;

FIG. 5 is a perspective view of an exemplary gap tensioner;

FIG. 6 is a front elevation view of the gap tensioner of FIG. 5, in aretracted position;

FIG. 7 is a front elevation view of the gap tensioner of FIG. 5, in anextended position;

FIG. 8 is a front elevation view of the gap tensioner in FIG. 5, in anextended and tilted position;

FIG. 9 is an exploded perspective view of the gap tensioner of FIG. 5;

FIG. 10 is a front elevation view of the gap tensioner of FIG. 5 showingan internal cable routing path;

FIG. 11 is a perspective view of an alternative embodiment of a gaptensioner;

FIG. 12 is a perspective view of a linkage of the gap tensioner shown inFIG. 11;

FIG. 13 is a schematic top plan view of the gap tensioner of FIG. 11,showing an internal cable routing thereof;

FIG. 14 is a front elevation view of an alternative gap tensionerlinkage in a retracted position;

FIG. 15 is a front elevation view of the alternative gap tensionerlinkage of FIG. 14, in a partially extended position;

FIG. 16 is a front elevation view of the alternative gap tensionerlinkage of FIG. 14, in an extended position;

FIG. 17 is a schematic perspective view of an exemplary gap tensioneractuated by a mechanical screw;

FIG. 18 is a schematic perspective view of an exemplary gap tensionerhaving a linkage incorporating variable-rate springs;

FIG. 19 is a schematic perspective view of the gap tensioner of FIG. 18with a portion removed to show the linkage in more detail;

FIG. 20 is schematic perspective view of an alternative spring for usewith the gap tensioner of FIG. 18;

FIG. 21 is a graph illustrating the stress-strain properties of theligaments in a human knee joint;

FIG. 22 is a perspective view of an exemplary actuating instrument;

FIG. 23 is a perspective view of a gap tensioner coupled to theactuating instrument of FIG. 22;

FIG. 24 is a side elevation view of the instrument of FIG. 22 in aretracted position;

FIG. 25 is a side elevation view of the instrument of FIG. 22 in anextended, unloaded position;

FIG. 26 is a side elevation view of the instrument in FIG. 22 in atensioned position;

FIG. 27 is a perspective view of an exemplary actuating instrument;

FIG. 28 is a perspective view of a gap tensioner coupled to theactuating instrument of FIG. 27;

FIG. 29 is a side elevation view of the instrument of FIG. 27 in aretracted position;

FIG. 30 is a side elevation view of the instrument of FIG. 27 in anextended, unloaded position;

FIG. 31 is a side elevation view of the instrument in FIG. 27 in atensioned position;

FIG. 32 is a perspective view of an exemplary actuating instrument;

FIG. 33 is a perspective view of a gap tensioner coupled to theactuating instrument of FIG. 32;

FIG. 34 is a side elevation view of the instrument of FIG. 32 in aretracted position;

FIG. 35 is a side elevation view of the instrument of FIG. 32 in anextended, unloaded position;

FIG. 36 is a side elevation view of the instrument in FIG. 32 in atensioned position;

FIG. 37 is a perspective view of an exemplary actuating instrument in aretracted position;

FIG. 38 is a perspective view of the actuating instrument of FIG. 37 inan extended position;

FIG. 39 is an enlarged view of a portion of FIG. 37;

FIG. 40 is a perspective view of an exemplary actuating instrumentcoupled to a gap tensioner;

FIG. 41 is a cross-sectional view of the actuating instrument of FIG.40;

FIG. 42 is a side elevation view of the actuating instrument of FIG. 40:

FIG. 43 is a perspective view of an exemplary actuating instrumentcoupled to a gap tensioner, in combination with a remote display;

FIG. 44 is a perspective view of an exemplary actuating instrumentcoupled to a gap tensioner, in combination with a remote display;

FIG. 45 is a perspective view of a human knee joint showing analternative gap tensioner inserted therein;

FIG. 46 is a perspective view of the human knee joint showing anotheralternative gap tensioner inserted therein;

FIG. 47 is view of the interior aspect of the human knee joint having agap tensioner inserted therein;

FIG. 48 is a view of the anterior aspect of a human knee jointillustrating the process of augmenting a ligament thereof;

FIG. 49 is a view of the anterior aspect of the human knee jointillustrating the process of releasing a ligament thereof;

FIG. 50 is a view of the anterior aspect of the human knee joint havinga varus angulation;

FIG. 51 is a view of the anterior aspect of the joint of FIG. 50,showing correction of the varus angulation through release of the medialcruciate ligament;

FIG. 52 is a view of the medial aspect of the human knee joint having agap tensioner inserted therein, in combination with a tensile memberused to augment or replace the lateral cruciate ligament;

FIG. 53 is a view of the anterior aspect of the human knee joint shownin FIG. 52;

FIG. 54 is a view of the lateral aspect of the human knee joint of FIG.52;

FIG. 55 is a view of the medial aspect of the human knee joint having agap tensioner inserted therein, in combination with a tensile memberused to augment or replace the medial cruciate ligament;

FIG. 56 is a view of the anterior aspect of the human knee joint shownin FIG. 55;

FIG. 57 a view of the lateral aspect of the human knee joint of FIG. 55;

FIG. 58 is a perspective view of a human knee joint having a kneeendoprosthetic implanted, in combination with a tensile member used toreplace or augment the medial cruciate ligament;

FIG. 59 is a view of the anterior aspect of the human knee joint,illustrating a first step in a total knee arthroscopy;

FIG. 60 is a view of the lateral aspect of the joint of FIG. 59;

FIG. 61 is a view of the anterior aspect of the human knee joint of FIG.59, illustrating a second step in a total knee arthroscopy;

FIG. 62 is a view of the lateral aspect of the joint of FIG. 61;

FIG. 63 is a view of the anterior aspect of the human knee joint of FIG.59, illustrating a third step in a total knee arthroscopy, with a gaptensioner inserted;

FIG. 64 is a view of the lateral aspect of the joint FIG. 59;

FIG. 65 is a view of the anterior aspect of the human knee joint of FIG.52 in flexion, illustrating a fourth step in a total knee arthroscopy,with the gap tensioner inserted;

FIG. 66 is a view of the lateral aspect of the joint of FIG. 65;

FIG. 67 is a view of the anterior aspect of the human knee joint of FIG.59 in flexion, illustrating a fifth step in a total knee arthroscopy;

FIG. 68 is a view of the lateral aspect of the joint of FIG. 67;

FIG. 69 is a perspective view of the human knee joint of FIG. 59,showing a marking device positioned within the joint;

FIG. 70 is another view of the medial aspect of the joint in FIG. 69,showing the patella in place;

FIG. 71 is a perspective view of the joint in FIG. 69, showing thepatella in place;

FIG. 72 is a perspective view of a cutter guide block;

FIG. 73 is a view of an anterior aspect of the human knee joint inflexion, with the cutter guide block of FIG. 72 in place;

FIG. 74 is a view of the medial aspect of the human knee joint having agap tensioner inserted therein; and

FIG. 75 is a perspective view of the human knee joint having a gapsensor inserted therein and tracking markers attached thereto;

FIG. 76 is a view of the anterior aspect of a human knee jointillustrating an alternative process of augmenting a ligament thereof;

FIG. 77 is a view of the anterior aspect of a human knee jointillustrating an alternative process of augmenting a ligament thereof;

FIG. 78 is a view of an anterior aspect of the human leg in extension,with tracking markers superimposed thereon;

FIG. 79 is a view of a medial aspect of the human leg of FIG. 78 inflexion;

FIG. 80 is a view of a medial aspect of the human leg of FIG. 78 inflexion, with a gap tensioner inserted in the knee joint and trackingmarkers attached thereto;

FIG. 81 is a view of an anterior aspect of the human leg of FIG. 80 inextension;

FIG. 82 is a schematic perspective view of a human knee joint having agap tensioner and trial condyle element inserted therein; and

FIG. 83 is a schematic perspective view of a human knee joint having agap tensioner and trial condyle element inserted therein.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings wherein identical reference numerals denotethe same elements throughout the various views, FIG. 5 depicts anexemplary gap tensioner 10 (alternatively referred to as a “jack”) whichis useful for balancing a gap a human knee joint as part of a total kneearthroscopy. In one aspect, the gap tensioner 10 may be described ashaving the ability to constrain or fix four degrees of freedom of a kneejoint while permitting controlled movement of two degrees of freedom.

The gap tensioner 10 comprises a baseplate 12 and a top plate 14interconnected by a linkage 16. The linkage 16 and the gap tensioner 10are movable between a retracted position in which the top plate 14 liesclose to or against the baseplate 12, and an extended position in whichthe top plate 14 is spaced away from the baseplate 12. As described inmore detail below, a mechanism is provided to actuate the linkage 16 inresponse to an actuating force in order to separate the baseplate 12 andthe top plate 14 in a controllable manner.

Solely for purposes of convenient description, the gap tensioner 10 maybe described as having a length extending along a lateral direction “L”,a width extending along an axial direction “A”, and a height extendingalong a vertical direction “H”, wherein the lateral direction, the axialdirection, and the vertical direction are three mutually perpendiculardirections.

The baseplate 12 includes a generally planar tibia interface surface 18.The baseplate 12 may include pin holes 20 for the purpose of receivingalignment pins (not shown) which would be driven into bone during asurgical procedure. The baseplate 12 includes a gap tensioner coupler 22having a first interface 24. In the illustrated example, the firstinterface 24 is configured as a threaded socket.

The top plate 14 includes a generally planar femur interface surface 26.The top plate 14 is mounted to the linkage 16 in such a manner that itcan freely pivot about pivot axis 28. The pivot axis 28 is parallel tothe tibia interface surface 18 and the femur interface surface 26, andin the illustrated orientation is parallel to the axial direction A. Thegap tensioner 10 may be configured to permit use with the patella inplace. This may be achieved by a careful selection of its dimensions andphysical configuration. More specifically, an overall width of the gaptensioner 10 parallel to direction A in FIG. 5 may be selected to fitbetween a patella and either the medial cruciate ligament or the lateralcruciate ligament so the device can be inserted into the knee joint.Additionally, the gap tensioner coupler is positioned at or near thedistal end of the baseplate 12 and is oriented so that it extends alongand protrudes in the axial direction “A”.

FIGS. 6-8 illustrate the construction and operation of the gap tensioner10 in more detail. In this embodiment, the linkage 16 is configured as apair of links 30 each having a lower end 32 and an upper end 34. Theupper ends 34 are joined together such that they can pivot about thepivot axis 28, thus forming a “X” or “V” configuration. The lower ends32 are mounted to the baseplate 12 such that they can slide in thelateral direction. Thus assembled, movement of the lower ends 32 awayfrom each other retracts or lowers the height of the gap tensioner 10,and movement of the lower ends 32 towards each other extends or raisesthe height of the gap tensioner 10. Accordingly, in use, an actuatingforce may be applied to the lower ends 32 to move them towards eachother, thus extending the top plate 14 away from the baseplate 12. Thelinkage 16 has predetermined kinematic properties, or stated anotherway, the ratio of displacement of the top plate 14 to input displacementis known and can be plotted a graph, for the entire range of motion.

FIG. 6 illustrates the gap tensioner 10 in the retracted position, andFIG. 7 illustrates the gap tensioner in the extended position. In allpositions, the top plate 14 is free to pivot about the pivot axis 28.FIG. 8 shows an example of the top plate 14 in a “tilted” position, orstated another way, with the femur interface surface 26 not parallel tothe tibia interface surface 18.

FIG. 9 illustrates a structure of the linkage 16 in more detail. Inparticular it shows the links 30 as well as a pivot pin 35 which servesto connect the upper ends 34 of the links 30 as well as to join thelinks 30 in a pivoting connection to the top plate 14.

In this embodiment, the lower end 32 of each link 30 has a roller 36mounted thereto. The rollers are received in tracks 38 formed in thebaseplate 12. This permits low-friction operation of the linkage 16.

Various means are possible for applying an actuating force to thelinkage 16. In the example shown in FIGS. 9 and 10, the linkage 16 iscable-actuated. One of the links 30 incorporates a cable anchor recess40 which receives a first end of the cable (not seen in FIG. 9). Thecable 42 is routed through the interior of the baseplate 12, exiting thegap tensioner coupler 22, as seen in FIG. 10. Thus routed and assembled,a tensile actuating force applied to the cable 42 will move the lowerends 32 of the links 30 closer together.

FIGS. 11-13 illustrate another exemplary gap tensioner 110. The gaptensioner 110 is similar in overall construction to the gap tensioner 10described above. Elements of the gap tensioner 110 not explicitlydescribed may be considered to be identical to corresponding elements ofthe gap tensioner 10.

The gap tensioner 110 includes a baseplate 112, top plate 114, and alinkage 116. In this embodiment, the linkage 116 is configured as a pairof links 130 each having a lower end 132 and an upper end 134. The lowerends 132 are mounted to the baseplate 112 such that they can slide inthe lateral direction. The lower ends 132 of the links 130 are receivedin sliders 144 which are in turn received in slots or tracks (notvisible) and the baseplate 112.

FIG. 13 illustrates cable routing within the baseplate 112. In thisexample, two separate cables 142 are provided, one cable beingterminated in each of the sliders 144.

FIGS. 14-16 illustrate an alternative linkage 216 comprising links 230,which may be substituted for the linkages described above. In thislinkage 216, one of the links 230 includes a cam 246 around which acable 242 is wrapped. The cam 246 is shaped such that as the linkagemoves from a retracted position (FIG. 14) towards an extended position(FIG. 16), the force-versus-displacement characteristics of the linkage216 change. Stated another way, the effective leverage of the cable 242changes as the linkage 216 moves through its range of motion. Forexample, the cam may be shaped such that a greater force is required toprovide a given deflection as the device moves towards extendedposition.

FIG. 17 illustrates another example of a gap tensioner 310. The gaptensioner 310 is similar in overall construction to the gap tensioner110 described above. Elements of the gap tensioner 310 not explicitlydescribed may be considered to be identical to corresponding elements ofthe gap tensioner 110.

The gap tensioner 310 includes a baseplate 312, top plate 314, and alinkage 316. In this example, the linkage 316 is configured as a pair oflinks 330 each having a lower end received in a slider 344 which is inturn mounted for sliding movement in the baseplate 312. A linearactuating element 348 such as the illustrated threaded shaft is mountedin the baseplate configured such that rotating movement of the actuatingelement 348 causes lateral sliding of the sliders 344, in turn actuatingthe linkage 316.

FIGS. 18 and 19 illustrate another exemplary gap tensioner 410. The gaptensioner 410 is similar in overall construction to the gap tensioner 10described above. Elements of the gap tensioner 410 not explicitlydescribed may be considered to be identical to corresponding elements ofthe gap tensioner 10.

The gap tensioner 410 includes a baseplate 412, top plate 414, and alinkage 416. The linkage 416 is configured as a pair of links 430 eachhaving a lower end 432 pivotally connected to the baseplate 412. Upperends 434 of the links 430 are pivoted to each other and to the top plate414. Each of the links 430 is a telescoping assembly and is providedwith one or more springs 450 which are arranged so as to urge thelinkage 416 towards an extended position. The springs 450 may beconfigured to have a variable rate. In one example, the springs 450and/or the geometry of the associated link 430 may be arranged to have aconstant force-displacement characteristic. Stated another way, a forceacting in the extension direction may be constant or substantiallyconstant regardless of the position of the top plate 414. In thisexample, no actuating force is required to operate the device. To thecontrary, the device may be compressed, placed in the working position,and then released to apply a working force.

FIG. 20 illustrates an alternative link 431 which may be substituted forthe links 430. This link 431 has a plurality of spring members 433formed therein and is a single integral, monolithic, or unitary elementwhich serves as both a telescoping link and a spring.

As noted above, the gap tensioner 10 is useful for balancing the gap ina human knee joint when performing a total knee arthroscopy. The use ofthe gap tensioner 10 may be better understood by considering thecharacteristics of the human knee joint, particularly of the soft tissue(e.g. ligaments). FIG. 21 is a representative diagram of knee joint gapheight versus applied extension load, similar to a stress-strain plot.In FIG. 21, the solid line is representative of properties of aperfectly elastic member (e.g. a rubber band). The dashed line isrepresentative of the properties of a hypothetical infinitely rigidmember. The dotted line is representative of the properties of a humanknee joint ligament. It can be seen that the ligament is quite stiff andexhibits a low elongation to failure. The vertical portion of the dottedline indicates the range of motion where a minimal applied load willtake up all available slack in the ligament. The slope of the gapheight/load curve then rapidly transitions through the arcuate corner inthe dotted line, to a very rigid characteristic. Given these properties,it will be apparent that the application of a relatively small load willensure that the ligament is at full extension. In one example, anextension load of about 300 N or less may be applied. It will beunderstood that the chart in FIG. 21 is general in nature, and thatspecific ligaments in specific joints may have different magnitudes ofslack available, or stated another way, the length of the verticalsegment of the dotted line will vary from joint to joint and ligament toligament. For example, in one patient's knee joint, all slack may betaken up at a relatively small gap height such as 9.5 mm. In anotherpatient's knee joint, all slack may be taken up at a relatively largerheight such as 20 mm.

Numerous instruments may be provided which are suitable for applyingactuation loads of this magnitude to the gap tensioner 10, as well asindicating, measuring, or recording physical properties of the gaptensioner 10 such as position, applied load, and/or tilt position.

FIGS. 22-26 illustrate an exemplary actuating instrument 500 for usewith the gap tensioner 10. The actuating instrument 500 includes abarrel 502. The distal end of the barrel 502 includes an instrumentcoupler 504 defining a second interface 506 complementary to the firstinterface 24 of the gap tensioner 10. In the illustrated example, thesecond interface 506 is configured as external threads.

The proximate end of the barrel 502 is connected to an actuatingassembly 508 including a handle 510, a lever 512, and actuating linkage514, and a load setting mechanism 516.

The actuating instrument 500 is configured to be coupled to the gaptensioner 10 by joining their mutual couplers 22, 504, to receive thecable 42 as described above (not shown), and to apply an actuating load,that is a tensile load, to the cable 42, thus actuating the gaptensioner 10.

The actuating instrument 500 may include some means for measuring orindicating displacement of the gap tensioner 10. In the illustratedexample, the handle 510 carries a movable pointer 518 which pivotsrelative to a scale 520. The pointer 518 is arranged to contact orotherwise be driven by the cable in operation, thus driving pointermovement. The scale 520 may be calibrated to directly indicate the “gapheight” (i.e. the distance between the tibial and femoral surfaces 18,26) of the gap tensioner 10.

The lever 512 is pivoted to the handle 510 and coupled to the actuatinglinkage 514 and the load setting mechanism 516. Operation of the lever512 causes the linkage 514 to apply tensile force to the cable 42 (notshown). The actuating force is applied through a spring element 522which is a portion of the load setting mechanism 516. Preload of thespring element 522 may be set using an adjuster 524 such as theillustrated threaded knob. Accordingly, there is a definite adjustableforce-displacement characteristic of the actuating instrument 500. Theactuating linkage 514 has predetermined kinematic properties, or statedanother way, the ratio of displacement of the cable 42 to inputdisplacement of the lever 512 is known and can be plotted a graph, forthe entire range of motion. The kinematic properties of the actuatinglinkage 514 can be configured to have a predetermined relationship tothe kinematic properties of the linkage 16 of the gap tensioner 10described above. In one specific example the kinematic properties of theactuating linkage 514 may be configured to have an inverse relationshipto the kinematic properties of the linkage 16. That is, the ratios ofinput to output displacement for the linkage 514 and the linkage 16would be inverse to each other for each position in the range ofmovement. This would result in a 1:1 output/input displacement ratio forthe entire mechanical system. This may be referred to as the actuatinginstrument 500 and the gap tensioner 10 having “inverse kinematics”relative to each other. With such a relationship, the actuatinginstrument 500 would provide in essence no mechanical advantage. Thishas the result that a unit deflection of the lever 512 results in a unitdeflection of the top plate 14, and a unit force applied to the lever512 results in an equal unit force being applied to the gap tensioner10.

Operation of the actuating instrument 500 is explained in more detailwith reference to FIGS. 24-26. FIG. 24 shows the actuating instrumentwith the lever 512 in a released position. FIG. 25 shows the lever 512in an intermediate position in which the cable is displaced and the gaptensioner 10 is partially extended, but no appreciable load is appliedto the gap tensioner 10, other than overcoming friction and other minorforces. This corresponds generally to the vertical segment of the dottedline graph in FIG. 21.

FIG. 26 shows the lever 512 in a fully actuated position in which thecable is not displaced any further appreciable amount, but an actuatingload (i.e. tension) is applied to the cable. It will be understood thatthe absolute position of the lever 512 relative to the body 510 whenfull preload is applied to the gap tensioner 10 will vary depending onthe actual gap height. The load setting mechanism 516 allows theactuating load to be accurately displayed and/or controlled. Forexample, observation or measurement of the displacement of the springelement 522, with the spring rate being known, gives the force beingapplied. Alternatively, the adjuster 524 may be used to set the preloadon the spring element 522 such that the desired actuating load isrequired to be applied in order to bring the spring element 522 to aknown position, for example a fully compressed position.

FIGS. 27-31 illustrate another exemplary actuating instrument 600 foruse with the gap tensioner 10. The actuating instrument 600 includes abarrel 602 with an instrument coupler 604 at its distal end. Theproximate end of the barrel 602 is connected to an actuating assembly608 including a handle 610, a lever 612, actuating linkage 614, and aload setting mechanism 616. The lever 612 carries a movable pointer 618which pivots relative to a scale 620 in order to indicate displacement.

Operation of the actuating instrument 600 is similar to that of theactuating instrument 500. As seen in FIGS. 29-31, the instrument 600 canbe moved from a released position, through an extended but unloadedposition, and finally to a fully actuated, loaded position as shown inFIG. 31.

FIGS. 32-36 illustrate another exemplary actuating instrument 700 foruse with the gap tensioner 10. The actuating instrument 700 includes abarrel 702 with an instrument coupler 704 at its distal end. Theproximate end of the barrel 702 is connected to an actuating assembly708 including a body 710, a handle 712, actuating linkage 714, and aload setting mechanism 716. The device may include a movable indicator718 which shows displacement against a scale 720. The linkage 714 isdirectly actuated by pressure of the load setting mechanism 716 which isset by the position of the handle 712. In this example, the handle 712is a threaded member connected to a threaded rod.

The actuating instrument 700 is operated by turning the handle 712,compressing the spring element 722 of the load setting mechanism 716,thus applying force to the linkage 714, which is translated to tensionapplied to the cable (not shown). Operation of the actuating instrument.As seen in FIGS. 34-36, the handle 712 can be rotated to varycompression of the spring element 722, moving the actuating instrument700 from a released position, through an extended but unloaded position,and finally to a fully actuated, loaded position as shown in FIG. 36.

FIGS. 37-39 illustrate another exemplary actuating instrument 800 foruse with the gap tensioner 10. The actuating instrument 800 includes abarrel 802 with an instrument coupler 804 at its distal end. Theproximate end of the barrel 802 is connected to an actuating assembly808 including a handle 810, a lever 812, actuating linkage 814, and aload setting mechanism 816. Operation of the actuating instrument 800 issimilar to that of the actuating instrument 500.

FIGS. 40-41 illustrate another exemplary actuating instrument 900 foruse with the gap tensioner 10. The actuating instrument 900 includes abarrel 902 with an instrument coupler 904 at its distal end. Theproximate end of the barrel 902 is connected to a housing 908 includinga handle 910, an operating knob 912, and a load setting mechanism 916.

The load setting mechanism 916 includes a spring element 922 having afirst end 952 configured to be coupled to a cable (not shown) and asecond end 954 connected to threaded plug 956. The threaded plug 956engages complementary threads of the operating knob 912. Rotation of theoperating knob 912 causes a tensile load to be applied to the springelement 922. The tensile load is proportional to the displacement of theoperating knob 912. As seen in FIG. 42, the housing 908 may be markedwith a scale 958 which shows the applied actuating load for measured gapsizes.

FIG. 43 illustrates another exemplary actuating instrument 1000 for usewith the gap tensioner 10. The actuating instrument 1000 includes abarrel 1002 with an instrument coupler 1004 at its distal end. Theproximate end of the barrel 1002 is connected to an actuating assembly1008 including a lever 1012. The interior of the actuating assembly 1008includes an appropriate mechanism (not shown) such as an actuatinglinkage similar to those described above. The internal mechanism isoperable to apply an actuating load to the gap tensioner 10 in responseto movement of the lever 1012. The actuating instrument 1000 includes anelectronic data transmitter, shown schematically at 1060. Thetransmitter 1060 may operate over a wired or wireless connection. Theactuating instrument 1000 and/or the tensioner 10 are supplied with anappropriate combination of transducers (not shown) to detect physicalproperties such as force, tilt angle, and/or applied load and generate asignal representative thereof. For example, the tensioner 10 may beprovided with sensors operable to detect the magnitude of extension(i.e. “gap height”), the angle of the top plate about the pivot axis(i.e. varus/valgus), and/or the applied force in the extensiondirection. Nonlimiting examples of suitable transducers include straingages, load cells, linear variable differential transformers (“LVDT”),rotary variable differential transformers (“RVDT”), or linear or rotaryencoders or resolvers. (Alternatively, the gap tensioner 10 may beprovided with simple visual scales, not shown, for displacement/gapheight and/or tilt angle, or may include a mechanical linkage, notshown, which can transmit movement representative of tilt angle to amechanical or electronic actuating instrument). The transmitter 1060 isoperable to transmit the signal. A remote display 1062 is configured toreceive the signal and produce a display 1064 of the transducer data. Asone example, the remote display 1062 may be embodied in a conventionalportable electronic device such as a “smart phone” or electronic tabletwith suitable software programming.

In use, the remote display 1062 permits the surgeon to observe thephysical properties of the gap tensioner 10 in real time as theactuating instrument 1000 is used to operate the gap tensioner 10.

FIG. 44 illustrates another exemplary actuating instrument 1100 for usewith the gap tensioner 10. The actuating instrument 1100 includes abarrel 1102 with an instrument coupler 1104 at its distal end. Theproximate end of the barrel 1102 is connected to an actuating assembly1118. The interior of the actuating assembly 1118 includes anappropriate driving mechanism such as an electrically-powered linearactuator 1114. The driving mechanism 1114 is operable to apply anactuating load to the gap tensioner 10, through cable 42. The actuatinginstrument 1100 includes an electronic data transmitter, shownschematically at 1160, and may include an appropriate electrical powersource such as a battery (not shown). The transmitter 1160 may operateover a wired or wireless connection. The actuating instrument 1110and/or the gap tensioner 10 are supplied with an appropriate combinationof transducers as described above with respect to actuating instrument1000, such as force transducer 1116, to detect one or more physicalproperties of the gap tensioner 10 and generate a signal representativethereof. The transmitter 1160 is operable to transmit the sensor signal.A remote display 1162 is configured to receive the signal and produce adisplay 1164 of the transducer data. As one example, the remote display1162 may be embodied in a conventional portable electronic device suchas a “smart phone” or electronic tablet with suitable softwareprogramming.

In use, the remote display 1162 permits the surgeon to observe thephysical properties of the gap tensioner 10 in real time as theactuating instrument 1100 is used to operate the gap tensioner 10Optionally, the actuating instrument 1100 may incorporate a trackingmarker 1162. It includes one or more tracking points (not individuallyillustrated) which may be configured as transmitting antennas,radiological markers, or other similar devices. Using an appropriatereceiving device, described in more detail below, the position andorientation of the receiving device to the tracking marker 1162 may bedetermined by receipt and analysis at the receiving device of signalstransmitted by the tracking marker 1602.

In the example described above, the gap tensioner 10 is intended to beused for a total knee arthroscopy and is sized and shaped to be insertedinto the human knee joint into span the entire gap across both condyles.Other configurations are possible. For example, FIG. 45 shows analternative gap tensioner 1210 inserted between the tibia T and femur Fof a human knee joint J. It can be seen that one condyle of the tibiahas been cut away and that the gap tensioner is sized and configured tobe inserted into the gap above the cut-away condyle, from the medialaspect of the joint.

FIG. 46 shows another alternative gap tensioner 1310 which has onemovable top plate 1314 positioned under one condyle and one fixed block1315 positioned under the other condyle.

The gap tensioner 10 is especially useful for adjusting the soft tissuelateral tension balance of a human knee joint. Referring to FIG. 47, agap tensioner 10 is shown inserted in an extension gap EG between thefemur F and the tibia T. The gap tensioner 10 pivots freely about pivotaxis 28 as described above. The tilt angle of the top plate 14 may bemanipulated by selective augmentation and/or release of the lateralcruciate ligament or it the medial cruciate ligament. FIG. 48illustrates a process of augmentation in which an artificial tensilemember 1400 secured with anchors 1402 is passed through the femur F andtibia T, spanning the lateral aspect of the extension gap. The term“anchor” as it relates to element 1402 refers to any device which iseffective to secure a tensile member 1400 passing therethrough.Nonlimiting examples of anchors 1402 and include washers, screw plates,ferrules, and swage or crimp anchors. Properly tensioned, this tensilemember 1400 replaces or augments tension provided by the natural lateralcruciate ligament. The augmentation shown in FIG. 48 is trans-osseous,but other forms of augmentation are possible. For example, FIG. 76illustrates a process of augmentation in which an artificial tensilemember 1401 secured with anchors 1403 spans the lateral aspect of theknee joint J. The tensile member 1401 may have both ends anchoreddirectly to the femur F and tibia T. Alternatively, as seen in FIG. 77,the tensile member 1401 may have its ends anchored to the components ofa knee arthroplasty 1407, which components are in turn anchored to thefemur F and tibia T. As yet another alternative (not shown), one end ofa tensile member may be anchored directly to the femur F or tibia T,with the other end indirectly anchored, for example it may be anchoredto an arthroplasty element which is in turn anchored directly to theopposite bone of the joint. As yet another alternative, a tensile membermay be anchored directly or indirectly to the fibula. FIG. 49illustrates a process of release in which a ligament (in this examplethe lateral cruciate ligament LCL) is partially severed to releasetension thereon. Either action, augmentation or release, would changethe balance of tension acting on the joint J and thus change the tiltangle (varus or valgus).

FIGS. 50 and 51 illustrate how the tilt angle (varus or valgus) may bemanipulated. FIG. 50 shows the joint J having a varus angulation. It canbe seen that central axes 1404, 1406 of the tibia T and femur F,respectively are not coaxial, but define an oblique angle therebetween.FIG. 51 shows a result of releasing the MCL, i.e. effectivelylengthening it and/or releasing its tension. It can be seen that thecentral axes 1404, 1406 are coaxial. This type of adjustment may use anycombination of augmentation and/or release and may be used to correctvarus or valgus angulation.

Various methods are known for augmentation of the soft tissues. As notedabove, one method involves the use of an artificial tensile member suchas a suture, cable, or filament, suitably anchored in tension. Examplesof this type of device are illustrated in FIGS. 52-57.

FIGS. 52-54 illustrate a tensile member 1400 fixed by anchors 1402 androuted through the human knee joint J across the lateral aspect of theextension gap e.g. in order to replace or augment the lateral cruciateligament (not shown).

FIGS. 55-57 illustrate a tensile member 1400 fixed by anchors 1402 androuted through the human knee joint J across the medial aspect of theextension gap e.g. in order to replace or augment the medial cruciateligament (not shown).

FIG. 58 illustrates a human knee joint J having an endoprosthetic 1408of a known type implanted therein. The endoprosthetic 1408 includes atibial component 1410 and the femoral component 1412. The joint J alsoincludes a tensile member 1400 fixed by anchors 1402 and routed throughthe knee joint J across the medial aspect of the extension gap in orderto replace or augment the medial cruciate segment (not shown).

A method for using the gap tensioner an instrument will now be describedwith reference to FIGS. 59-73.

Initially, FIGS. 59, 60, a tibial cut (cutting plane labeled 1) is madein the tibia T. This may be done using conventional techniques. Ideally,the tibial cut 1 makes a surface that is normal to vertical in thecoronal plane and at a slight angle (e.g. 0° to 7°) to vertical in thesagittal plane.

In a second step, FIGS. 61, 62 a distal femoral cut (cutting planelabeled 2) is made in the femur F. This may be done using conventionaltechniques. Ideally the distal femoral cut 2 makes a surface that isnormal to a “perfect” anatomical mechanical axis between the center ofthe knee and the femoral head.

In the third step, FIGS. 63, 64, the gap tensioner 10 is insertedbetween the femur F and the tibia T and used to conduct a soft-tissuebalancing procedure. The gap tensioner 10 is moved towards an extendedposition which has the effect of driving the femur F and the tibia Tapart from each other, defining the extension gap EG. The gap tensioner10 is conformable to lateral angulation. That is, the free pivoting ofthe top plate 14 about the pivot axis 28 permits the knee joint J totake up whatever varus or valgus angulation naturally occurs.

The specific varus or valgus angulation will be governed by the relativelengths of the medial cruciate ligament and the lateral cruciateligament. The extension of the gap tensioner drives both of theseligaments to their full extension. The preload of the tensioner 10provides a margin to ensure full extension.

Once desired extension, for example full extension. of both ligaments isachieved, the lateral angulation (varus or valgus) can be observed,measured, and/or recorded. Measurement may be by various means. In oneexample, dimensions and angles may be measured directly using measuringinstruments.

Once the lateral angulation is determined, the extension gap EG may bebalanced. To balance extension gap, soft-tissue is augmented and/orsoft-tissue is released, using the procedure described in detail abovewith reference to FIGS. 47-51. In the example shown in FIGS. 61 and 62,the knee joint J exhibits valgus angulation (knock-knee) when loaded bythe gap tensioner 10. Correction may be performed by augmenting themedial cruciate ligament and/or releasing the lateral cruciate ligament.The balance procedure is done until the extension gap EG is uniform(i.e. no varus or valgus angulation).

Once the extension gap EG has been balanced, resulting in the conditionshown in FIGS. 63 and 64, they gap tensioner 10 may be used to establishthe flexion cuts.

Referring to FIGS. 65 and 66, the gap tensioner 10 is placed in theflexion gap FG and tensioned to the same load as used to establish theextension gap EG. This may be carried out with the patella and/orpatellar tendon (not shown) in place (i.e., the patella is not requiredto be everted and may be in the normal anatomical position).

Once full extension of both ligaments is achieved, the characteristicsof the flexion gap FG (magnitude and angulation) can be observed,measured, and/or recorded. The soft tissue is not altered in this step.It will be understood that the magnitude (height) and/or tilt of theflexion gap FG are likely to be different from the extension gap EG. Itwill be further understood that is desirable for the flexion gap FG tobe parallel and equal to the extension gap EG. In the example shown inFIGS. 65 and 66, the knee joint J exhibits valgus angulation(knock-knee) when loaded by the gap tensioner 10. Furthermore, since theposterior cut has not yet been made, the flexion gap FG is smaller thanthe final required amount. It can be seen from FIG. 65 that in order tocreate a balanced flexion gap FG, the posterior cut must remove thedifferent amounts of material from the two condyles of the femur F.

The posterior cut (cutting plane labeled 3) is then made so as to createthe desired (balanced) flexion gap FG′, as seen in FIGS. 66 and 67. Thegap tensioner 10 may be utilized to accurately mark the desired cuttingplane. Referring to FIGS. 69-71, the gap tensioner 10 is left insertedinto the flexion gap FG, maintaining tension on the soft tissue whilereferences are marked for the posterior cut.

In the example shown in FIGS. 69-71, a marking attachment 1500 isprovided which includes a body 1502 of a predetermined height extendingbetween first and second ends 1504, 1506. The first end 1504 is providedwith means for attachment to the base plate 12 of the gap tensioner 10.For example, a dovetail joint (not shown) may be used. The second end1506 is provided with suitable marking implement such as the illustratedtwo spaced-apart marking tips 1508 positioned along the line parallel tothe tibial surface 18 of the base plate 12. The marking attachment 1500may further include a handle 1510 to allow for surgical manipulation.

The marking attachment 1500 is used by attaching it to the baseplate 12with the joint J in flexion and then using the marking tips 1508 tostrike or impress two indentations which serve as a reference formounting of a cutter guide block described below. This may be carriedout with the patella “P” in place (not everted), as seen in FIGS. 70 and71. It will be understood that the geometry of the marking attachment1500 ensures that the two indentations lie on a line parallel to thetibial cut in the tibia T. Accordingly, this provides a basis for makinga posterior cut which is automatically ensured to be parallel to thetibial cut.

FIG. 72 illustrates a suitable cutter guide block 1520 of a known type.The cutter guide block 1520 includes, among other features, a posteriorcut guide surface 1524 and at least one pair of space-apart guide holes1526. The guide holes 1526 are configured to receive guide pins orscrews (not shown) which may be driven into bone to hold the cutterguide block 1520 in position while the posterior cut guide surface 1524is used to guide the blade of a bone saw (not shown). Fundamentally, inorder to produce the desired cut, the posterior cut guide surface 1524is placed parallel to and coplanar with or slightly spaced away from theposterior cut plane 3.

It will be understood that the guide holes 1526 lie along a line whichis parallel to the posterior cut guide surface 1524, at a known distancefrom the posterior cut guide surface 1524. Accordingly, in order toaccurately position the cutter guide block 1520, it is a straightforwardmatter to select the height of the marking attachment 1500, and thus theposition of the marking tips 1508, taking into account the distancebetween the guide holes 1526 and the posterior cut guide surface 1524,and the desired final height of the flexion gap FG. FIG. 73 shows thecutter guide block 1520 in-place against the femur F, ready to make theposterior cut 3.

Once a posterior cut 3 is made, the knee joint J as a balanced flexiongap FG which matches the extension gap EG. Subsequently, conventionalsteps may be carried out to complete the total the arthroscopy, such asmaking chamfer cuts, trial fitting the endoprosthetic components, andcementing the endoprosthetic components.

The devices described above have additional usefulness in relatedsurgical procedures, particularly in determining the proper bone entrypoints for artificial tensile members used to augment the naturalligaments. FIG. 74 is a view of the medial aspect of the human kneejoint J having a gap tensioner 10 inserted therein. The view shows thejoint with three different positions of the femur F superimposed—fullextension labeled 0°, an intermediate position labeled 45°, and fullflexion labeled 90°. Shown also on the femur F is a curve 1600 whichrepresents the locus of the instantaneous axis of rotation (“IAOR”) ofthe joint J for each position. The IAOR changes throughout the jointrange of motion. This happens because during joint motion the femoralcondyle translates in the anterior/posterior directions and the femoralcondyle rides against the tibia in a cam motion.

For best surgical outcomes, it is preferable to route an artificialtensile member through a hole in the femur F passing through curve 1600.The exact location of this curve 1600 can be difficult to determineusing prior art methods. The apparatus described herein can provide amethod for accurately locating this curve to serve as a drilling target.

In one example, the location method may be carried out using theinstrument 1100 described above. As noted above, the instrument 1100 mayinclude appropriate sensors for determining the extension load, thevarus/valgus tilt angle, and the gap height. In order to locate thecurve 1600, the instrument 1100 would be coupled to a gap tensioner 10inserted into the knee joint J between the tibia T and the femur F,after making the tibial cut but prior to making the distal femoral cut.In one option, a predetermined extension load would be applied by theinstrument 1100. The joint J would then be moved through the range offull extension to full flexion, while using the sensors to determine thegap height and varus/valgus angle in each location within the range ofmotion. This data may be translated through empirical means to derivethe location of the curve 1600.

Optionally, this method may be performed after the tibial and femoralcuts have been made, by providing a trail condyle element of anarthroplasty. For example, FIG. 82 illustrates a trial condyle element1800 inserted between the femur F and the gap tensioner 10. Thisconfiguration permits a continuous range of joint motion after thedistal femoral cut is made. As another example, FIG. 83 illustrates atrial condyle element 1802 inserted between the femur F and the gaptensioner 10. This configuration permits a continuous range of jointmotion after the distal femoral and posterior formal cuts are made.

In another option, the instrument 1100 will be controlled so as toprovide a fixed gap height. The joint J would then be moved to the rangeof full extension of full flexion, while using the sensors to determinethe change in extension load and the varus/valgus angle in each locationwithin the range of motion. This data may be translated throughempirical means to derive the location of the curve 1600.

In a related method, described with respect to FIG. 75, the instrument1100 described above may be used with other apparatus not only to derivethe location of the curve 1600 but to guide the surgeon to drill a holein a proper location along the curve. The instrument 1100 would becoupled to the gap tensioner 10 inserted into the knee joint J betweenthe tibia T in the femur F, after making the tibial cut prior to makingthe distal femoral cut. A tracking marker 1602 would be attached to thetibia T. The tracking marker 1602 is attached to the tibia T in such away that it has a substantially fixed position and orientation relativeto the tibia T. It includes one or more tracking points 1604 which maybe configured as transmitting antennas, radiological markers, or othersimilar devices. Using an appropriate receiving device such as theillustrated instrumented, receiver-equipped cordless drill 1606, theposition and orientation of the cordless drill 1606 relative to thetracking marker 1602 may be determined by receipt and analysis at thecordless drill 1606 of signals transmitted by the tracking marker 1602.Tracking marker 1602 and appropriate receivers are known within thestate-of-the-art. Additionally, a second tracking marker 1608 would beattached to the femur F in such a way that as a substantially fixedposition orientation relative to the femur F. Again, the positionorientation of the cordless drill 1606 relative to the tracking marker1608 may be determined.

Once the gap tensioner 10, actuating instrument 1100, and trackingmarkers 1602 and 1608 are implanted, the joint J would then be moved tothe range of full extension of full flexion, while monitoring theposition of tracking markers 1602 and 1608. The path swept out by thetracking marker 1602 and 1608 is representative of the movement of thecondyle of the femur against the gap tensioner 10. The data representingthe path may be translated using empirical means to determine theposition of the curve 1600.

Once a position of the curve 1600 is determined, the tracking markers1602 and 1608 may be used to guide the cordless drill 1606 to drill ahole passing through the curve 1600, with the drill bit 1610 extendingan appropriate angle. This guidance is possible becauseintercommunication between the cordless drill 1606 and the trackingmarker 1602 and 1608 will give the relative to position and orientationof the cordless drill 1606 to those markers. The drilling guidance maybe provided in the form of information displayed on the remote display1162 described above. For this purpose, 2-way data communications may beprovided between and among the cordless drills 1606 (or other surgicalinstrument), the tracking markers 1602 and 1608, the actuatinginstrument 1100, and the remote display 1162.

This method is especially helpful in providing drilling guidance becauseit provides the benefits of a surgical navigation system, which istypically large, complex, and expensive, using simple inexpensive localrelative position information. For example, the absolute position andorientation of the knee joint J is not required to perform the step ofmoving the joint J through the range of motion and then guiding thecordless drill 1606 to drill a hole at the appropriate location andorientation.

In another related method, described with respect to FIGS. 78-81, theinstrument 1100 described above may be used in combination otherapparatus to improve accuracy of alignment of the knee joint J. FIG. 78illustrates the knee joint J between the femur F and tibia T, the talusjoint “U” between the tibia T and the foot “O”, and the acetabulofemoraljoint “B” between the femoral condyle “C” and the pelvis “P”. FIG. 78also illustrates an axis 1405 passing through the femoral condyle C andthe talus joint U. The ability to measure lateral position of the kneejoint J relative to the axis 1405 is helpful in determining angulation(i.e. varus/valgus) of the knee joint J. For purposes of thismeasurement, the center of the knee joint J and the lateral sense isconsidered to be the midpoint between the medial and lateral condyles.For example, in general a nominal varus/valgus angulation occurs whenthe center of the knee joint J is coincident with the axis 1405.Different patients may exhibit variations in the nominal position.Furthermore, a surgically desirable varus/valgus angulation may bedifferent from nominal this may be done, for example to correct a defectin the patient's anatomy.

Various methods are possible for establishing the location of the axis1405. One method involves the use of an atomic old tracking markers or“navigation” systems. FIG. 76 illustrates schematically a first trackingmarker 1700 disposed at the center of the femoral condyle C, a secondtracking marker 1702 located at the center of the knee joint J, and athird tracking marker 1704 located at the center of the talus joint U.The tracking markers 1700, 1702, 1704 are representative of the positionof the associated anatomical structures. In practice, the trackingmarkers may be physical or virtual. For example, surgical navigationsystems are commercially available which have the capability ofmeasuring the position of hardware tracking markers and/or generatingvirtual tracking markers through the use of medical imaging methods.

Once the tracking markers 1700, 1702, 1704 are established, the kneejoint J may be placed in flexion as shown in FIG. 79. The complete legmay then be moved laterally to the left and the right alternatively,thus generating a position track for each of the tracking markers 1700,1702, 1704. This movement will cause rotation of the leg about the axis1405 which intersects the first tracking marker 1700 and the thirdtracking marker 1704. The axis 1405 may be analytically constructed, forexample by observing that the first and third tracking marker 1700, 1704exhibit little to no movement while the second tracking marker 1702sweeps out an arc. Computation will show the center of this arc lies onthe axis 1405.

The function of the tracking markers 1700, 1702, 1704 may be replaced inwhole or in part with local, relative navigation devices such as thetracking markers described above. This is shown in FIGS. 81 and 81. Inthis example configuration, a tracking marker 1608 (described above) isattached to the femur F in such a way that as a substantially fixedposition orientation relative to the femur F.

Another tracking marker 1708 is coupled to the talus joint U in such away that as a substantially fixed position orientation relative to thefemur F. For example, it may be coupled t the talus joint U using aC-shaped ankle clip or ankle clamp 1710 which may be resilient,spring-loaded, etc.

Finally, the gap tensioner 10 is inserted into the knee joint J andcoupled to the actuation instrument 1100 having a tracking marker 1162as described above. Alternatively, the gap tensioner 10 may be providedwith a built-in tracking marker (not shown).

A receiving device such as remote display 1062 is configured to receivethe signals and or otherwise track the positions of the tracking markers1162, 1608, and 1708 and to store, manipulate, and/or display theposition data.

Once the gap tensioner 10, actuating instrument 1100, and trackingmarkers 1162, 1608, and 1708 are in place, the leg would then be movedto a flexion position. The complete leg may then be moved laterally tothe left and the right alternatively, while monitoring the position oftracking markers 1162, 1608, and 1708, thus generating a position trackfor each of the tracking markers 1162, 1608, and 1708. The axis 1405 maybe analytically constructed, for example by observing that the trackingmarkers 1162, 1608 exhibit little to no movement while the trackingmarker 1708 sweeps out an arc. Computation will show the center of thisarc lies on the axis 1405.

Once a position of the axis 1405 is determined, the leg can be placedback in extension and tracking markers 1602 and 1608 may be used tomeasure lateral position of the knee joint J relative to the axis 1405.As noted above, this information is helpful in determining angulation(i.e. varus/valgus) of the knee joint J.

The apparatus and method described herein have numerous advantages overprior art apparatus and techniques.

The gap tensioner enables patella-in-place gap balancing during totalknee arthroplasty. By allowing the patella (and other soft tissue aroundthe knee space) to remain in its anatomical position during thebalancing procedure, a more accurate and anatomically relevant gap canbe established.

Furthermore, due to its non-intrusive nature, the gap tensioner canenable in-situ gap balancing by means of soft tissue releases (to openone side of the gap relative to the other to make it more “rectangular”and less “trapezoidal”) and tension ligament augmentation (to close oneside of the gap by tightening or augmenting ligaments to make it more“rectangular” and less “trapezoidal”).

The foregoing has described apparatus and methods for knee gaptensioning. All of the features disclosed in this specification, and/orall of the steps of any method or process so disclosed, may be combinedin any combination, except combinations where at least some of suchfeatures and/or steps are mutually exclusive.

Each feature disclosed in this specification may be replaced byalternative features serving the same, equivalent or similar purpose,unless expressly stated otherwise. Thus, unless expressly statedotherwise, each feature disclosed is one example only of a genericseries of equivalent or similar features.

The invention is not restricted to the details of the foregoingembodiment(s). The invention extends, or to any novel one, or any novelcombination, of the steps of any method or process so disclosed.

What is claimed is:
 1. A knee gap tensioning apparatus comprising: a gaptensioner including: a baseplate; a top plate; a linkage interconnectingthe baseplate and the top plate and operable to move the gap tensionerbetween retracted and extended positions; and wherein the top plate ispivotally connected to the linkage so as to be able to freely pivotabout a pivot axis.
 2. The apparatus of claim 1 wherein the linkagecomprises links that move in an axial direction in response to lateralmovement.
 3. The apparatus of claim 1 wherein the linkage is operated byone or more cables.
 4. The apparatus of claim 3 wherein the cable isrouted at least partially inside the baseplate.
 5. The apparatus ofclaim 3 wherein the cable passes over a cam surface defined by one ofthe links.
 6. The apparatus of claim 1 wherein the linkage includesrollers received in tracks of the baseplate.
 7. The apparatus of claim 1wherein the linkage includes bearing plates slidably received in tracksof the baseplate.
 8. The apparatus of claim 1 wherein the linkagecomprises one or more springs.
 9. The apparatus of claim 8 wherein thesprings are configured to produce a constant force acting towards theextended position.
 10. The apparatus of claim 8 wherein the springs areintegral to the links
 11. The apparatus of claim 1 wherein the linkageis driven by a screw mechanism.
 12. The apparatus of claim 1 furtherincluding a marking attachment.
 13. The apparatus of claim 1 wherein thebaseplate includes a gap tensioner coupler positioned at or near thedistal end of the baseplate 12 and is oriented so that it extends alongand protrudes in an axial direction.
 14. The apparatus of claim 1 incombination with an actuating instrument operable to apply actuationforce to the linkage.
 15. The apparatus of claim 14 wherein the gaptensioner and the actuating instrument have an inverse kinematicrelationship.
 16. The apparatus of claim 14 wherein the actuatinginstrument has independent indicators of displacement and applied force.17. The apparatus of claim 14 wherein the actuating instrument isconfigured to apply an actuating force through a spring element.
 18. Theapparatus of claim 14 wherein the actuating instrument is configured toindicate deflection of the spring element.
 19. The apparatus of claim 14wherein: the gap tensioner includes at least one sensor operable tomeasure a physical property of the gap tensioner and to generate asignal indicative of the property; and The actuating instrument includesa transmitter operable to receive the signal and transmit the signal.20. The apparatus of claim 19 further including a remote device operableto receive the signal and display an indication representative of thephysical property.
 21. The apparatus of claim 19 wherein the physicalproperty is displacement, tension and/or tilt angle.
 22. The apparatusof claim 14 wherein the actuating instrument includes a powered actuatoroperable to apply the actuating force.
 23. The apparatus of claim 14wherein: the gap tensioner includes a tensioner coupler having a firstinterface; and the actuating instrument includes an actuating instrumentcoupler having a second interface complementary to the first interface.24. A knee gap tensioning apparatus comprising: a gap tensionerincluding: a baseplate; a top plate; a linkage interconnecting thebaseplate and the top plate and operable to move the gap tensionerbetween retracted and extended positions; and wherein the top plate ispivotally connected to the linkage so as to be able to freely pivotabout a pivot axis; two or more tracking markers, at least one of whichis coupled to the gap tensioner; and an electronic receiving device,wherein the receiving device is operable in combination with thetracking markers to determine a position and orientation of each of thetracking markers relative to the electronic receiving device.
 25. Theapparatus of claim 24 wherein at least one of the tracking markersincludes a C-shaped ankle clip.
 26. The apparatus of claim 24 wherein atleast one of the tracking markers is contained in the gap tensioner. 27.The apparatus of claim 24 in combination with an actuating instrumentcoupled to the gap tensioner and operable to apply actuation force tothe linkage.
 28. The apparatus of claim 26 wherein at least one of thetracking markers is contained in the actuating instrument.
 29. Theapparatus of claim 27 wherein the actuating instrument includes apowered actuator operable to apply the actuating force.
 30. Theapparatus of claim 26 wherein: the gap tensioner includes at least onesensor operable to measure a physical property of the gap tensioner andto generate a signal indicative of the property; The actuatinginstrument includes a transmitter operable to receive the signal andtransmit the signal; and a remote device operable to receive the signaland display an indication representative of the physical property.